Toner-based document imaging, such as electrophotographic, ionographic, magnetographic, and similar imaging techniques, generally involves forming an electrostatic or magnetic image on a charged or magnetized photoconductive plate or drum, brushing the plate or drum with charged or magnetized toner, transferring the image onto a substrate such as paper, polyester film, or the like, and fusing the toner onto the substrate using heat, pressure, and/or a solvent. Using this technique, relatively inexpensive images can be easily formed on a surface of the substrate.
Because toner-based imaging is a relatively quick and inexpensive technique for producing copies of images, the technique is often employed to produce documents that were traditionally formed using other forms of printing or imaging—e.g., impact printing, off-set printing presses, or ink-jet printing. For example, in recent years, toner-based imaging has been employed to produce financial documents, such as personal checks, stocks, and bank notes; legal documents such as wills and deeds; medical documents such as drug prescriptions and doctors' orders; and the like. Unfortunately, because the image is formed on the surface of the substrate, documents produced using toner-based imaging techniques are relatively easy to forge and/or duplicate. Recently, specialty toners with unique security features have been developed to address the growing problem of document fraud that presently exists in a wide variety of markets.
U.S. Pat. No. 5,714,291, issued to Marinello et al. on Feb. 3, 1998, discloses a toner that includes submicron ultraviolet sensitive particles, which emit light of a specific ultraviolet wavelength(s). A document can be verified by using a scanner that reads the specific ultraviolet wavelengths(s). Requiring use of an ultraviolet scanner is generally undesirable because it requires additional equipment and adds significant cost to a forgery analysis.
United States Publication No. US2003/0054277, in the name of Fujikura, dated Mar. 20, 2003, discloses a dual-component toner containing phosphorescent pigment and a binder resin. The toner includes phosphorescent pigment having a particle diameter falling within a range of between 0.01 μm and 9.0 μm. According to the reference, if the particle diameter is larger than 7.0 μm, the phosphorescent pigment tends to be separated from within the toner particle. If the toner includes a colorant or a developing agent, the toner is formed in a multi-step process, which includes forming a master batch, which in the case of a toner including a colorant is prepared by sufficiently dispersing the coloring agent in a suitable amount of the binder resin, and adding the remaining binder resin to the master batch. Then, the mixture is melted and kneaded, following by a pulverizing and classification process. Although this toner and process appear to work for certain applications, the particle size of the phosphorescent material is relatively small, which reduces an amount of brightness of the phosphorescent material. In addition, the process requires a separate master batch step, which requires additional time and expense.
United States Publication No. US2010/0062360, in the name of Victor, dated Mar. 11, 2010 discloses methods of making ink toners for use in electrostatic imaging. The reference notes that current methods of making optically variable ink toners for use in electrostatic printing are not operable, and that current methods destroy the pigments present in the ink toner. United States Publication No. US2010/0330487, in the name of Veregin et al., dated Dec. 30, 2010, states that while commercial phosphorescent pigments exist, they are too large to be incorporated into toner particles and therefore it has not been possible to directly prepare phosphorescent electrophotographic prints. Veregin further states that both chemical and conventional toner processes currently available will fail to incorporate these large pigments. Veregin et al. purports to overcome this problem by coating the phosphorescent material, which is relatively time consuming and expensive.
For the foregoing reasons, improved methods and apparatus for forming documents having a phosphorescent image using toner-based processing, which are relatively easy and inexpensive, are desired.